As shown in FIG. 1, a conventional lamp-type luminous device includes a luminous chip 1 that emits light when a voltage is applied thereto, and first and second leads 2 and 3 that are connected to cathode and anode of the luminous chip 1, respectively, and made of a conductive metal material to apply a voltage to the luminous chip 1. The luminous chip 1 is attached to a cup-shaped pad formed on an end of the first lead 2 with a conductive adhesive and bonded to the second lead 3 via a wire 4. Further, the luminous chip 1 is molded with a molded portion 5 made of an insulating material such that it can be protected from the outside. At this time, the first and second leads 2 and 3 are partially exposed to the outside such that they can apply a voltage to the luminous chip from the outside.
The luminous device so configured has been recently implemented into a white LED applicable to a variety of fields as well as a monochromatic luminous device including the three primary colors, i.e. red (R), green (G) and blue (B). Therefore, the application field of a luminous device gradually tends to expand into a next-generation illumination system capable of substituting for an incandescent bulb, fluorescent lamp or street lamp as well as a luminous source for use in a backlight of a general display unit. Accordingly, there are advantages in that the illumination system using a luminous device does not need an inverter circuit and a core stabilizer, has a simpler lighting circuit than a general fluorescent lamp, and has low maintenance costs since it has lower power consumption and life at least ten times greater than that of the fluorescent lamp.
The luminous device so configured has been recently implemented into a white LED applicable to a variety of fields as well as a monochromatic luminous device including the three primary colors, i.e. red (R), green (G) and blue (B). Therefore, the application filed of a luminous device gradually tends to expand into a next-generation illumination system capable of substituting for an incandescent bulb, fluorescent lamp or street lamp as well as a luminous source for use in a backlight of a general display unit. Accordingly, there are advantages in that the illumination system using a luminous device does not need an inverter circuit and a core stabilizer, has a simpler lighting circuit than a general fluorescent lamp, and has low maintenance costs since it has lower power consumption and life at least ten times greater than that of the fluorescent lamp.
Recently, a study on such a luminous device for use in an illumination system has been vigorously conducted. However, since maximum luminous efficiency of a luminous device and heat dissipation characteristics correlate with each other, the heat dissipation problem should be solved if the luminous device is to be used for the illumination system. That is, if the luminous device is used for the illumination system, heat generated in the chip is increased and the chip in the luminous device is thus subjected to greater thermal stress. Accordingly, the product reliability is decreased and the life span of the product is also shortened. In particular, the lamp-type luminous device shown in FIG. 1 dissipates heat only via heat conduction of the metallic lead frames. There is a problem in that the thermal stress imposed on the luminous device is increased.
To solve such a problem, a heat dissipation member such as heat sink or slug made of a metal material with excellent heat conductivity is mounted between the luminous chip and a substrate such that the thermal stress imposed on the luminous device has been successfully reduced to a certain degree.
However, due to limitation in the conductivity of metal and poor heat transfer characteristics at interfaces between the heat dissipation member and the substrate or luminous chip, the resultant heat conductivity is lowered. Thus, the thermal stress problem of the luminous device cannot be effectively solved. Further, there is another problem in that the electrical characteristics of the luminous device are deteriorated or luminous characteristics of the luminous device are changed since external foreign substances such as moisture penetrate into the luminous device through a pre-determined gap that may occur between the heat dissipation member and the substrate. Therefore, further increased luminous efficiency cannot be obtained by only such heat conduction of the heat dissipation member, and the increase in cooling load cannot also effectively solved.